linux-kernel - Re: [PATCH v2 RESEND 1/2] ARM: spectre-v2: Fix potential missing mitigations

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Message-ID: <20251028162825.x-4ryn3p@linutronix.de>
Date: Tue, 28 Oct 2025 17:28:25 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Xie Yuanbin <xieyuanbin1@...wei.com>
Cc: rmk+kernel@...linux.org.uk, linux@...linux.org.uk, rppt@...nel.org,
	vbabka@...e.cz, pfalcato@...e.de, brauner@...nel.org,
	lorenzo.stoakes@...cle.com, kuninori.morimoto.gx@...esas.com,
	tony@...mide.com, arnd@...db.de, akpm@...ux-foundation.org,
	punitagrawal@...il.com, rjw@...ysocki.net, marc.zyngier@....com,
	will@...nel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, liaohua4@...wei.com,
	lilinjie8@...wei.com
Subject: Re: [PATCH v2 RESEND 1/2] ARM: spectre-v2: Fix potential missing
 mitigations

On 2025-10-28 17:20:06 [+0100], To Xie Yuanbin wrote:
> The requirement is to invoke the mitigation callback of the right CPU.
> What about disabling preemption before getting the callback and doing
> the invocation?

Something like this:

diff --git a/arch/arm/include/asm/system_misc.h b/arch/arm/include/asm/system_misc.h
--- a/arch/arm/include/asm/system_misc.h
+++ b/arch/arm/include/asm/system_misc.h
@@ -20,8 +20,10 @@ typedef void (*harden_branch_predictor_fn_t)(void);
 DECLARE_PER_CPU(harden_branch_predictor_fn_t, harden_branch_predictor_fn);
 static inline void harden_branch_predictor(void)
 {
-	harden_branch_predictor_fn_t fn = per_cpu(harden_branch_predictor_fn,
-						  smp_processor_id());
+	harden_branch_predictor_fn_t fn;
+
+	guard(preempt)();
+	fn = per_cpu(harden_branch_predictor_fn, smp_processor_id());
 	if (fn)
 		fn();
 }

Sebastian